Do not show SMS SIM pick UI for Cell Broadcast Config change

If the user did not pick their default SIM subscription for
SMS, we were showing many dialogs to the user whenever
SmsManager#getSubscriptionId was called for cell broadcast
related APIs.

Instead, if we instantiate the SmsManager using
SmsManager.getDefault() and the user has not set a default,
use the default Phone and do not show SIM picker activity
(consistent with legacy implementation).

Bug: 129315610
Test: set up DSDS, disable eSIM operator in settings
Change-Id: I3cc4839632eede75c8943836432b07978d0efda0